This invention relates to breathable water-resistant fabrics and a process for making same, especially fabrics laminated with a microporous fluoropolymer, e.g. a microporous poly[ethylene-tetrafluoroethylene] ("ETFE") layer.
ETFE is a copolymer containing approximately equal numbers of ethylenic and tetrafluoroethylenic repeating units primarily linked alternately: --C.sub.2 H.sub.4 --C.sub.2 F.sub.4 --C.sub.2 H.sub.4 --C.sub.2 F.sub.4 --. Its flow temperature is between about 200.degree. C. and about 280.degree. C., depending upon the exact proportion of ethylenic to tetrafluoroethylenic repeating units, and on the molecular weight and structure of the polymer. Commercially available ETFE resin includes HOSTAFLON.RTM. (Hoechst, A. G.).
A fabric that is both water-resistant and breathable (i.e., permits air and water vapor, but not liquid water, to pass through) has obvious advantages for use in clothes and other applications. Polytetrafluoroethylene ("PTFE") has been used to make fabrics of this type, e.g. in GORETEX.TM. products.
U.S. Pat. No. 3,962,153 issued to Gore describes porous films consisting of highly stretched PTFE; PTFE pellets are melt extruded into films and then the films are stretched. The stretching process imparts porosity to the polymer films, the resulting film structure characterized by having nodes interconnected by fibrils; these films are anisotropic.
U.S. Pat. Nos. 3,679,614 (Shah, et al.), 4,342,636 (Chang, et al.), and 3,661,645 (Strier, et al.) describe other processes for making porous PTFE films.
U.S. Pat. Nos. 4,910,106 and 4,997,603, both issued to Kafchinski, et al., describe the formation of halogenated polymeric microporous membranes having improved strength. These membranes have a very narrow pore size distribution and good temperature and chemical resistance. A polyhalogenated copolymer, such as ETFE, having a very small particle size is blended with a binder polymer using a binder solvent that is a non-solvent for the copolymer and then a film is formed from the blend; subsequent heat treatment causes the copolymer particles to form a relatively continuous matrix. When the binder is extracted, a microporous film results. The disclosures of these two patents are hereby incorporated by reference herein.
U.S. Pat. No. 3,929,950 issued to Nakamura, et al., describes a method for forming a porous synthetic resin film using a stretching technique. The resin may be, for example, ETFE, PTFE and the like.
U.S. Pat. Nos. 4,623,670 and 4,702,836 both issued to Mutoh, et al., describe a porous membrane made of a fluorinated polymeric resin such a ETFE having a uniform porous structure and good properties. A chlorotrifluoroethylene oligomer must be used with the polymeric resin to form a microporous film by the disclosed method.